My 85 XJ6 has been sitting for about two years, just got it out yesterday and cleaned it up, everything seems to be working fine but when i took it around the block a couple times, i noticed the odo and trip odo wern't working, but the speedometer was working the whole time. Does anyone have an idea of whats goin on and how I should fix it?

 

Well thats different.
Usually the thing quits altogether and you need to replace the transducer on the transmission.
This one sounds like a mechanical problem inside.
However I am not sure of the extent of the internal electrics.
The speedo pops out from behind by gripping the front bezel with finger tip pressure
and turning slightly to the left. Wies disconnect and you can have a carefull
look or try a replacement. Not hard to do that one.

Rushing off to work now.
Check back later.

Cheers.

JustV12

 

Yeah, remove and open up the speedo. I don't really know what you'll see but perhaps you'll find the the odometer mechanism is just stuck....and a tiny drop of oil in the right place will free it off.....or something like that.

Or....remove it and send it to an instrument repair specialist.

Or...if all else fails get a used speedo. They're a dime-a-dozen on Ebay

Cheers
DD

 

ok, speedo is out, how do i go about opening it up? and are there any good instrument repairs places you guys know of?

 

9 years later.....I thought I'd chime in on this one, just in case someone(like me)comes across this problem and needs some info. My speedo works, but the odometer doesn't. When I did a search I noticed 99% of responses were dealing with "speedo not working". I went ahead and did the 12V and GRD checks. Everything is proper. Started(still will)to just replace the Transducer at the Trans., but strange enough, travel and gas usage info is registering on the trip computer. So somebody is sending PULSES to somebody. Well, I recently purchased 3 used speedo's in a package deal, 1 to perform surgery and 1 that's close to my present mileage. SURGERY--other than the wires going to the indicator bulbs of the speedo, 3 wires enter the unit. One 12V at ignition, one GRD. and one yellow control(pulse) wire. the wires connect to a small solid state control board. 5 wires leave the board, 2 go to the speedo. coils and 3 go to the odometer AC stepper motor. I installed one of the replacement speedo's, same problem. Strange that both might have inoperative boards or stepper motors or frozen number tumblers. (37 yrs., maybe not so strange)As I reflect, 12V going to Speedo. and yellow wire(spliced to the trip computer)delivering speed information, then the odometer stepper motor should be moving. MUST BE MECHANICAL!................maybe??? I'll update.

 

I have the exact same issue. I consider it lucky in a sense because my car does not do more than 5000 miles a year. Saves a bundle on insurance.

Kidding aside. I am sure this is mechanical because i can see mine attempting to tick over and just stop. Also I notice that when I press the trip button the odometer starts working again. When you dive into this please take lots of pictures and do a write up. It would help me for sure! I'd have messed with it myself before but I don't have any spares.

 

I came across some info from a poster which said that the “tumblers” are old and cranky. Solution would be to grease the mechanism with a little lithium, problem is this though, I used a small, fine flat blade to un-bend the “ears” surrounding the rear of the ring around the glass. I’m telling you, the metal is some kind of space age material, took awhile, got it apart(the surgery donor). My problem is this, being a little obsessive compulsive, I’m not comfortable tearing up the case to get in and grease the tumblers. I have no plan to sell my car, but if I did, who would believe the car had 88,000mi. in 2020 after seeing or knowing the unit had been tampered with? Man! I’m stuck here. I will send some pic’s of the innards and update.

 

send the original to:

https://speedycables.com/

they are in the UK. There are many gauge rebuilders in the US but many of them give you a bunch of bs, and Speedy Cables doesn't. In fact if you contact them by email, they might even tell you how to fix it.

I had a tachometer in my '65 S type that was intermittent, and it was not the tach-generator causing it.
I contacted them and they told me to check inside for a little spring tab that needed to make contact. Indeed the spring tab was not making full contact. Bent it a little and problem fixed. They even sent me a blue jewel indicator I needed for the speedo at no charge. They are a great business.

 

Thank you, very much. This forums has saved me thousands of dollars with “how to’s” for the DIY. I’ll update when the time arrive’s.

 

Thanks again, Jose. I contacted SPEEDYCABLES by email, they responded in less than 24hrs. They acknowledged that the unit has probably failed and advised me mail the unit to them. Cost of repair...$93US and cost to ship back to me. I will probably do that. But first, I’m going to continue addressing the 17.5V floating through my electrical system. I searched this forum and found that it is not always a faulty voltage regulator problem within the alternator which causes a consistent or intermittent 17+ volts. It seems poor grounding points can be the bug-a-boo. The poster with the similar problem which I am experiencing was advised to remove the alternator from the mounting surfaces and clean the matting surfaces until they are “shiny”. In the words of the solution giving poster “these surfaces haven’t seen the light of day since the manufacture date”. Those surface areas where the alternator mounts, are an integral part of the “charging circuit” current flow. Man!! That’s some good info. So, the poster did as was requested AND inspected all ground points AND replaced any substandard wires connected with the alternator circuit. 14.2-14.4V consistent. NOW, I said ALL THAT to say, there’s an IC board located in the speedo/odo case. The only “chip” on the board functions as a voltage regulator and signal “smoother”. It accepts the varying voltage of 11-14.5V signal coming in from the green wire and regulates it to approx. 7.5V regardless of fluctuations. Now IC COMPONENTS do not like static, incorrect voltage or incorrect current.( see where we are going) It’s possible the board could receive 17.5V and decide it is no longer going to cooperate. My trip computer innards had a blown diode(cracker in half). I’m going to remove transducer, attach ground to the case(schematics don’t show it grounding at Trans., but can’t hurt)confirm 12V and grd. at back of speedo, spin the transducer and monitor voltage(AC) at the 2 black and 1 red wire going into the motor. It is possible for the board to feed the speedo. mechanism and not output voltage to the odo motor. Below are pix of speedo innards. One picture show the board w/chip...


Next one is motor and worm gear which spins the “tumblers”.




Next one is of the white bushing glued to the axle of the “tumblers” so tight it keeps tumblers close together you can not manual rotate them. If there is no voltage going to the motor while spinning transducer with a drill then off to SPEEDYCABLES she/he(?). I live in Ca., they make us talk like that.lol. goes. I’ll update.
-Tony M.

 

Tony,
that looks more involved than I would have imagined.
$93. sounds reasonable. In the US others would have quoted you over $200.
Tell them to also calibrate it to the size of the tires you have, assuming they can do that.

There is a voltage stabilizer for the gauges,
But I don't know if that has anything to do with the voltage issue you have. Check the factory service manual and the S57 Electrical Guide.

In my website I have a link to a page which discusses the trip computer. Also free downloads of the S57 Electrical Guide and all factory service manual sections.
Jag Upgrades Home

 

Yeah, I agree it gets kinda deep. You know the old line “if you understand how something works you can understand how it fails”. I’m really trying to research and understand how my car works. I love this car, I have a little education in Electronics so the problems don’t set me back, too much. But, I still learn DAILY from you and the others here. It really humbled me to be reminded of the current flow being compromised by alternator and bracket mounting points. Thanks.

-Tony M.

I purchased another Trip Computer, it worked, initially, then started displaying “a variety of Alien’s”. I believe 17.5V is their Planet!

 

yes and while you're at it, clean the mating surfaces of the ground strap from the body to the transmission-engine where they join at the bell housing. Located on the passenger side under the car.

I'm sure you know already to disconnect the battery whenever doing any electrical jobs. It's an annoying back and forth but keeps the electricals safe.

 

Okay. I was wondering about the strap your referring to because the poster whom I was speaking of confirmed one of his ground issues was “a strap hanging down, unconnected, which should have been attached to the ground point at the back end of intake manifold”. I was like “I don’t think so!”.

I realize I’m off thread, but these issues do overlap. Just saw your GROUND STRAP product. I’ll go for it.

 

in the Series 3 XJ-6, (1979 to 1987), it is located under the car, bolted to chassis and to transmission bell housing to one of the bolts between 7 or 9 o'clock.

maybe Series 1 or 2 XJ have it at the exhaust manifold? I've never seen one there.

But near the firewall, intake side, there is also a group of 3 ground wires in ring terminals connected to the rear of the cylinder head with one bolt. And below that, difficult to see from above, there is another ground wire bolted to the block covered in grease.

At the firewall, on each side of the engine, there are two ALWAYS HOT posts with thick brown wires in ring terminals behind rubber boots that should be cleaned shiny. These posts cross the firewall into the interior where other hot wiring connects to. The battery needs to be disconnected to clean those.

 

Now you see what I mean? Been studying, researching and never came across the location of a ground point BELOW the collection of thin wire grounds congregated at rear cylinder head covered with oil. Thanks, again.

 

My son came up with a fix that resolved a plethora of oddities and a flat out failure to crank!!!

An added cable from the ground on the right wing to the alternator mount on my GM engine.
Cranked right up and a lot of gremlins vanished . Clue, the groun down under is not the best idea...

Carl

 

Poor grounds are a common malady on older cars in general. On British cars the much ballyhooed problems with the "Lucas, Prince of Darkness" electrics are almost always traced back to poor grounds and/or dirty connections/contacts.


I did the same on my car, Carl, except I used the air injection pump mount instead.

A lot of the V12s had the ground strap buried alongside the LH engine mount, exposed to all sort of yuck. Out of sight, out of mind....and difficult to access for cleaning if you DID think about it. Topside locations are much better

Cheers
DD

 

Good stuff folks. Going to the garage in a day or so to use all this useful info. Gotta give ya this GEM though, my JAG kinda reminds me of my old love experience, “Looks sooo Beautiful on the outside, but upon closer inspection, there was really a poor connection”, I’m just sayin.

 

on the subject of the trip computer displaying alien messages, I think Doug said that if you disconnect and reconnect it, it comes back to life.

you can try to pull it out using a thin guitar string sliding the string through the left and right ends and pulling carefully. .010 gauge is the string gauge I used once. (you can get them at Guitar Center or Sam Ash Music Stores for a dollar). There are two springy brackets, one on each side, you have to defeat them to be able to pull it out. Otherwise you have to pull the entire panel enough to get your hand behind it and to press the brackets towards the trip computer, and that requires a lot of dismantling.

Note that the string trick can also be used to pull the plastic cowl vent grille between the wipers. You slide the string under the grille and move it towards the center until you are stopped by the pin, then you pull up with both hands. You do that on each side. There are two pins. A lot easier than pulling the trip computer.